mozilla: Plug a leak

We were leaking SSIDs like crazy.

I really gotta get zbus into a useful state soon enough and oxidise
geoclue (#103) cause these issues waste so much time and also users'
resources until fixed.

Fixes #120.
3 jobs for fix-ssid-leak in 10 minutes and 14 seconds (queued for 9 minutes and 53 seconds)
Status Job ID Name Coverage
  Test
passed #670440
ubuntu-16.04

00:10:14

passed #670441
ubuntu-18.04

00:03:31

passed #670442
ubuntu-18.04-no-backend

00:02:53